1. Field of the Invention
The present invention relates to multi-shaft extruder screw bushings for conveying/mixing material in a multi-shaft extruder. More particularly, the present invention relates to a single flighted conveying/mixing screw bushings having only a single helically extending screw element.
2. Background Art
Screw conveying bushings for twin-screw extruders are well known. Generally, the screw bushings are generally 2 or 3-flighted bushings have 2 to 3 screw elements helically extending the length of the bushing. The crest of the screw elements are generally flat. These prior art screw bushings are manufactured such that side by side screw element crests generally mesh with each other when mounted in a twin screw extruder. The end walls of a standard screw bushing have flat surfaces. The end wall flat surface has a central annular section with two lobes extending diametrically opposite each other from the central section.
Each of the lobes has a truncated crest. Generally, two or more of the screw bushings are placed end to end to provide a continuous helical screw on each side by side twin screw extruder drive shaft. These screw bushings are generally used for conveying materials in the extruder.
A single flighted screw bushing is known for use to build up pressure generally at the end of the extruder. However, this type of screw bushing has a large arcuate crest that permits flow of product from one bushing to its side by side bushing as the above described 2 and 3-flighted screw bushings do. Thus, this known single flighted bushing is generally not used for the conveying/mixing of material.